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141.
Diane Lefebvre Jacqueline Pierre Yannick Outreman Jean-Sébastien Pierre 《Behavioral ecology and sociobiology》2007,61(11):1707-1715
The patch living rules of a pollinator, the bumblebee Bombus terrestris L., are studied here in the framework of motivational models widely used for parasitoids: The rewarding events found during
the foraging process are supposed to increase or decrease suddenly the tendency of the insect to stay in the current patch
and therefore to adjust the patch residence time to the patch profitability. The foraging behaviour of these pollinators was
observed in two environment types to determine their patch-leaving decisions. The rich environment was composed of male-fertile
flowers, offering pollen and nectar, and the poor one of male-sterile flowers, offering little nectar and no pollen. The experimental
design consisted of a patch system in which inflorescences were evenly arranged in two rows (1 m distance). Residence times
of foragers inside inflorescences and rows were analysed by a Cox proportional hazards model, taking into account recent and
past experience acquired during the foraging bout. Most of the results showed a decremental motivational mechanism, that is,
a reduction in the residence time on the inflorescence or in the row related to exploitation of flowers within inflorescences
and inflorescences within rows These results indicate that bumblebees tend to leave the patch using departure rules similar
to those found in parasitoids. The results also provide information on the memory, learning and evaluating capabilities of
bumblebees especially when rich and poor environments were compared. The patch-leaving mechanism suggested by this study is
consistent with the central place foraging theory. 相似文献
142.
Effect of indigenous bacterial activity on arsenic mobilization under anaerobic conditions 总被引:1,自引:0,他引:1
Batch biochemical leaching tests were carried out to investigate the mobility of arsenic from a contaminated soil collected from a French gold mining site. The specific objective of this research was to examine the effect of indigenous bacterial activity on arsenic mobilization under anaerobic conditions. In a first step, physical and chemical characterizations were performed to provide data concerning the liquid-solid partitioning and mobility of arsenic and other inorganic constituents. In a second step, batch bioleaching tests were conducted in shaker flasks to determine the effect of indigenous bacterial activity under different anaerobic conditions (i.e., addition of mineral nutrients and carbon sources) on arsenic mobilization. Results indicated that arsenic release during contact with deionized water was limited by its very low solubility in the interstitial solution and by the stability of the different arsenic compounds formed with the amorphous solid phases of the soil (mainly iron (oxy)hydroxides). However, an increased mobilization potential was observed over the long term under anaerobic conditions with indigenous bacterial activity enhanced by the addition of carbon sources. 相似文献
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144.
We investigated the seasonal patterns of denitrification rates and potentials in soil profiles along the topohydrosequence formed at the upland-wetland interface in three riparian wetlands with different vegetation cover (i.e., forest, understory vegetation, and grass). Denitrification was measured using the acetylene inhibition method on soil cores and slurries, which provided a means of comparing the relative activity of this process in different locations. We evaluated, on a seasonal basis, the respective importance of the vegetative cover and the hydromorphic gradient as factors limiting denitrification. Regardless of the season, vegetation type, or lateral position along each topohydrosequence in the riparian wetlands, strong significant gradients of both in situ and potential denitrification rates were measured within a soil profile. Results confirm that the upper organic soil horizon is the most active, when in contact with the ground water. In deeper soil horizons, denitrification activity was low (from 0.004 to 0.5 mg N kg(-1) dry soil d(-1)), but contributed significantly to the reduction of ground water NO3- load along the riparian ground water flowpath (from 9.32 to 0.98 mg NO3-N L(-1)). Along the soil topohydrosequence, the denitrifying community of the upper soil horizons did not vary significantly on a seasonal basis despite the large seasonal ground water fluctuations. Along each topohydrosequence, the denitrification-limiting factor gradually shifted from anaerobiosis to NO3- supply. In situ denitrification rates in the forested, understory vegetation and grass sites were not significantly different. This result emphasizes the importance of the topography of the valley rather than the vegetation cover in controlling denitrification activity in riparian wetlands. 相似文献
145.
Estimating parameters of neutral communities: from one single large to several small samples 总被引:3,自引:0,他引:3
The neutral theory of S. P. Hubbell postulates a two-scale hierarchical framework consisting of a metacommunity following the speciation-drift equilibrium characterized by the "biodiversity number" theta, and local communities following the migration-drift equilibrium characterized by the "migration rate" m (or the "fundamental dispersal number" I). While Etienne's sampling formula allows simultaneous estimation of theta and m from a single sample of a local community, its applicability to a network of (rather small) samples is questionable. We define here an alternative two-stage approach estimating theta from an adequate subset of the individuals sampled in the field (using Ewens' sampling formula) and m from community samples (using Etienne's sampling formula). We compare its results with the simultaneous estimation of theta and m (one-stage estimation), for simulated neutral samples and for 50 1-ha plots of evergreen forest in South India. The one-stage approach exhibits problems of bias and of poor differentiability between high-theta, low-m and low-theta, high-m solution domains. Conversely, the two-stage approach yielded reasonable estimates and is to be preferred when several small, scattered plots are available instead of a single large one. 相似文献
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147.
Towards a framework for assessment and management of cumulative human impacts on marine food webs
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Sylvaine Giakoumi Benjamin S. Halpern Loïc N. Michel Sylvie Gobert Maria Sini Charles‐François Boudouresque Maria‐Cristina Gambi Stelios Katsanevakis Pierre Lejeune Monica Montefalcone Gerard Pergent Christine Pergent‐Martini Pablo Sanchez‐Jerez Branko Velimirov Salvatrice Vizzini Arnaud Abadie Marta Coll Paolo Guidetti Fiorenza Micheli Hugh P. Possingham 《Conservation biology》2015,29(4):1228-1234
Effective ecosystem‐based management requires understanding ecosystem responses to multiple human threats, rather than focusing on single threats. To understand ecosystem responses to anthropogenic threats holistically, it is necessary to know how threats affect different components within ecosystems and ultimately alter ecosystem functioning. We used a case study of a Mediterranean seagrass (Posidonia oceanica) food web and expert knowledge elicitation in an application of the initial steps of a framework for assessment of cumulative human impacts on food webs. We produced a conceptual seagrass food web model, determined the main trophic relationships, identified the main threats to the food web components, and assessed the components’ vulnerability to those threats. Some threats had high (e.g., coastal infrastructure) or low impacts (e.g., agricultural runoff) on all food web components, whereas others (e.g., introduced carnivores) had very different impacts on each component. Partitioning the ecosystem into its components enabled us to identify threats previously overlooked and to reevaluate the importance of threats commonly perceived as major. By incorporating this understanding of system vulnerability with data on changes in the state of each threat (e.g., decreasing domestic pollution and increasing fishing) into a food web model, managers may be better able to estimate and predict cumulative human impacts on ecosystems and to prioritize conservation actions. 相似文献
148.
Pierre Canetto 《International journal of occupational safety and ergonomics》2013,19(2):141-153
Occupational noise specialists do not generally recommend hearing protection devices (HPDs) as a preferred solution to noise risk prevention. Nevertheless, these devices are widely used and are in fact often necessary. Selection of an HPD should take into account comfort and the capacity for perceiving external signals, when they are worn. Current European regulations require that HPD attenuation be considered, when comparing noise exposure to limit values. However, HPD attenuation is effectively unknown under real-world conditions. Some methods are designed to give approximate attenuation values and these provide results within a wide statistical range. Field measurement methods and current standards have been developed to deal with this situation. The specific characteristic of impulse noise requires establishment of dedicated criteria and tools for HPD selection and testing. This paper introduces a number of avenues for research, which could be of assistance in improving HPD selection, qualification and design. 相似文献
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